Infrared spectroscopic studies on polyethylene, 7. The use of the methyl deformation band for branch characterisation

Abstract

AbstractThe factors relating to measuring the position of the methyl deformation mode at about 1378 cm−1 with sufficient precision to permit its use for the identification of the different branches present in the various types of “linear” low density polyethylene(as manufactured by the copolymerization of ethylene and a 1‐alkene) have been examined systematically. With a data density of eight points per wavenumber, and the well established subtraction procedure with polymethylene or with a near‐linear polyethylene to remove the overlapping methylene deformation band, it is possible to achieve a precision of ±0,15 cm−1. This is ample to distinguish between methyl, ethyl, and butyl or hexyl branches, but not to characterise uniquely these last two. The use of Fourier self‐deconvolution to separate the methyl band has also proved very effective. The precision obtainable when these methods are applied to spectra measured with one data point per wavenumber is somewhat lower, but is still adequate for characterisational purposes. The results for a series of polymers containing ethyl branches at various concentrations suggest a small difference for the peak position for branches present in crystalline and amorphous regions.